This research project is directed towards a better understanding of the mechanisms underlying the changes in ionic conductance of nerve membranes that are responsible for the generation of electrical signals. The proposal has been divided into three sections. The first concerns an investigation of the possible interaction between selectivity-determining regions of ionic channels and kinetic and steady state properties of gating. This section is also involved with an assessment of the possible identity of the selectivity-determining region of the sodium channel with the receptor for tetrodotoxin (TTX). A number of biochemical isolation techniques rely on TTX binding as a means of identifying Na channel components. The second part utilizes chemical reagents capable of modifying membrane proteins in particular ways as a means of investigating: possible differences in the distribution of sodium and potassium channels in the membrane; the identification and possible labeling of a reactive group at the selectivity filter of sodium channels; and the localization of components involved in "slow" sodium inactivation, a process associated with the action of local anesthetics. The third area concerns the cellular basis for the action of volatile general anesthetics. We plan to investigate the modification of ionic conductance changes by halothane, ether, and related compounds, at clinically relevant concentrations. This proposal thus seeks an elucidation of basic excitability mechanisms in ways that will contribute to an understanding of the mode of action of a number of important toxins, neuropharmacological agents and anesthetics.